Resistive notes (2) - to shake or not to shake

Ah, that is the question.  Many emerging chemigramists have written to ask me, when I lay my photo paper in a tray of developer or fixer, do I agitate it there, in its 10 mm or so of liquid, or do I let it rest?  Does it even matter?  Let's approach this question by thinking about it for a moment.

It seems clear that a motion tangential to the surface of the paper (and of the liquid too, if not deep) will produce a shear stress acting on the paper in a manner to dislodge anything clinging there, if given enough time and enough agitation.  Now, to review, chemigram materials resident on the paper might include (1) hard resists, like varnish, (2) soft resists, like syrup, or (3) quite inviscid and nonadhesive fluids like the fixer or developer themselves, for example, or other household chemical agents that may be chosen for suspected properties.  But their rapid dislodgement is not always desirable; it really depends on the effect we seek.  In the case of inviscid, free-flowing fluid, we are usually quite content just to dip and pull, securing the signature mark of the enveloping chemical and moving on to other things.  But just for the record we show, in figure 1, what a shear stress might yield in such an evanescent situation, from one of my own works from 2009.  It's rather hard to reproduce, this effect, requiring a certain lightning-quick flick of the wrist, since the viscosity coefficient of waterlike materials is so small - so don't attempt this if you discourage easily.  Just think about it as a possibility.

figure 1

 

The choices and our ability to profit from them are more varied as we move up the rheology scale to tougher resists.  Some workers may favor a slow progressive erosion of the bonds between paper and resist, others may like it faster.  The difference between the two can be seen in the width of the resultant Mackie lines.  Testing this, we performed a simple experiment three times during the first week of November, using Ilford RC paper, somewhat impure Kodak developer and fixer (but normal for chemigrams), Golden MSA varnish, and common x-acto incisions, to compare a paper that received monitored agitation with one that was left unattended in the tray.  The time to withdrawal was twenty minutes, by which time the effects were amply demonstrated. 

figure 2a, agitated

We illustrate this by one of the runs - they were all similar - shown in figure 2a (with agitation) and 2b (stationary).  When we enlarge them and apply a scale (not shown in this post), we find a Mackie expansion of 10 mm in the stationary case vs 14 mm in the agitated one, a 40% increase that remains significant even if the crudeness of our measurements is discounted.

We can compute a velocity, for those who care, of 4.2 x 10 (exp -2) m/hr.  Not much, but not zero either.

figure 2b, stationary

At this rate, the Mackie line would circle the earth at the equator in a runtime of 3 x 10 (exp 8) hours, or 34,224 years, give or take.  So shaking the paper seems a good way to get where you want to go.  Patience helps too.

Mackie himself was never sure..

Collins, Florence H., 2010

Photoelastic fringe pattern

Obama solarized

Alexander Mackie arose at a meeting of the London and Provincial Photographic Association in 1885, as colleagues advanced theories about lines that sometimes appear around a figure or shape in a photograph, a bit like halos. "No, no, sir!" he cried. "That simply won't do. That doesn't fully explain it at all." For each theory brought forward to explain the mysterious lines, Mackie disproved it with a counter example. He showed pictures, he demonstrated his theses with objects, vases and tables. Optical illusions, effects of radiation, disparity between central and marginal rays of a lens, exhausted developer, nothing withstood his intellectual rigor. When the matter was revisited in subsequent meetings Mackie was again there. He haunted these meetings. He garnered a reputation: the guy with the lines nobody can explain. After thirty years of this - thirty years! - he could take no more, and wrote a letter to the august British Journal of Photography (64, 11-12, 1917) saying (in effect), "Hey, everyone associates these lines with my name as if the matter were settled, but that's far from the truth. We still haven't a clue."

If Mackie himself was never sure what a Mackie line was, no one else was quite sure either. But certain ideas have stuck, and have spread out in the world. In the field of photoelastic stress analysis, for example, they use the edge effect of pseudo-solarization (also known as Sabatier) to construct models of the stress distribution in materials; the lines of stress are called Mackie lines. You want to know where an I-beam will break, you find its Mackie lines.

In his Theory of Photographic Process (1942), C.E. Kenneth Mees was already able to describe Mackie lines as "the commonest adjacency effect" and said it was a white line formed at an abrupt enhancement of density at a border. Later, in his landmark monograph on photographic solarization (1997), William Jolly discussed a half-dozen border effects including Beck lines, Mach bands, Sabatier border lines and Mackie lines. He put Mackie lines in a special class very near to Sabatier border lines and (with a little arm waving) described a back-and-forth flow over the border of developer and reaction products and their excitatory or inhibitory effect on silver grains.

I've always thought highly of this explanation, but when I'm standing over my trays, poking at my paper, I can't help but feel otherwise for the case of chemigrams, which have had a somewhat closeted history since Cordier's discovery of them in 1956. The erosive appearance of border lines seen in chemigrams looks to be due to straightforward chemical attack, in developer and then in fixer, during the gradual, progressive removal of overlying resist. The developer darkens, the fixer lightens, each does its normal job, and the border recedes. At least this is the simplest explanation; the gentleman from Ockham taught us to always choose the simplest.

You could construct, or imagine, other scenarios. Trans-border diffusion of bromide, counter diffusion of developer, electromagnetic radiation collected in the exposed areas causing an inhibitory heating effect in adjacent areas, etc etc. Yet to me the evidence is merely suggestive at best, and the border appearance in chemigrams may not warrant such involuted theories anyway. This is because what we want to account for in chemigrams doesn't have the same origin as what we want to understand in other border situations, in Sabatier or in solarization - the phenomena arise differently.

I must confess though, at the end of the day the border effects in all these can be seductively similar. For that reason, for that similarity, we choose to retain the name Mackie line for the characteristic erosive line in chemigrams. Mackie wrote to the Journal about everyone using his name for these lines and said, "the connection has not arisen from any choice on my part, but was adopted merely as a convenient expression for avoiding an inconvenient descriptive formula of words." If he were alive Mackie would grumble a complaint to our blog, and we would know he's right, but it would change nothing.

The chemigram at top, Florence H., is pure Mackie lines.

Resistive notes (1)

Collins, 071210CH-1, detail

In the simplest chemigrams (the word 'simple' is deceptive, since these are often some of the most powerful works), form, body and color are applied in a direct way by merely dipping and dunking the photopaper in fixer or developer. To get more complex effects, one usually employs a resist of some sort. Resists are materials that block or delay the action of chemistry on a region of paper until a later moment, when surrounding areas will have already transformed away from their original state. When the resist is finally removed or erodes by degradation, chemical action can now begin in these areas as well, which because they have 'fallen behind' the others, will have a contrasted appearance. This is the source of much of the imagery in chemigrams.

Resistive materials are many and varied, as are the strategies for using them. What I like to call 'soft resists' are materials whose lifespan on the photopaper is quite limited, counted in seconds to a minute or so. Materials like white glue (polyvinyl acetate emulsion), corn syrup or other food products, tape, chewing gum, and clay are found in this category. The list extends, and among chemigramists it is a matter of some joy to identify new candidates for inclusion. Ideally, a resist should not totally resist, but instead should have a little give around its edges, so that as the resist begins ever so slightly to lift off, the paper beneath is quietly and progressively changed - and this may continue for a while - before the big moment when all or most of the resist at last raises itself and sloughs off. This creates drama and interest. In technical terms, what is left behind is a sequence of Mackie lines, or tidal marks of erosive history. They can be seen in the illustrations accompanying Rich's post of June 27, or better yet, in much of the work of the great Belgian artist, Pierre Cordier.

If we have soft resists, we must also have hard resists. Hard resists are materials that endure several orders of magnitude longer before leaving the photopaper, sometimes up to an hour. Several are known. Perhaps the most effective and reliable (as far as my knowledge allows) is mineral spirits-based synthetic varnish, and there are a number of them to choose from, some good, some not so good for various reasons. Some in fact inhibit others, if used on the same piece of photopaper.

By way of launching the discussion, here is an example of W&N ConserveArt varnish (green arrow) having thickened its activity to the point of quenching the normal spread of Liquitex Soluvar (red arrow), when the two varnishes were mixed together. The illustration is at 40 minutes of history. The Soluvar effects began to be evident at around 9 minutes along lines of incision (another story), while at that time there was no sign of ConserveArt activity. Then, insidiously, cracks appeared in the non-incised areas, while Soluvar effects seemed delayed. The cracks soon became larger and formed tilings, with tiny, characteristic Mackie lines. Comparison with other experiments led to the conclusion that this was ConserveArt activity. By now Soluvar activity had ceased altogether.

In notes to follow I will explore these and related topics, share observations from my studio, and try to find a basis to understand the mechanisms involved. For with understanding comes wisdom and with wisdom, art. Or something like that.